1. Field of the Invention
The present invention relates to a video signal processing apparatus, an enhancement gain generating method, and an enhancement gain generating program. More particularly, the invention relates to a video signal processing apparatus or the like which performs an enhancement process on a luminance signal to improve the sharpness of an image.
2. Description of the Related Art
Television receivers, video tape players, and DVD players in the related art have an enhancement function for improving the sharpness of an image, and a user can adjust an enhancement gain (enhanced amount) obtained by the function. However, an enhancement gain obtained by an adjustment stays fixed regardless of the content of an image. As a result, noises may be undesirably emphasized, for example, in flat signal regions, and a resultant image may have low quality.
There are enhancing techniques involving coring which employ a circuit performing no enhancement on noises having small amplitudes. However, since signals cannot be distinguished from noises, a problem arises in that enhancement is disabled also for small amplitudes or details of an image having no noise.
For example, JP-A-2007-318313 (Patent Document 1) discloses a proposed approach including the steps of calculating a histogram, detecting areas where the histogram shows significant changes as flat regions, and reducing the value of an enhancement gain in such flat regions. However, such an approach has problems when used for real-time processing, including the need for calculating a histogram of each screen in advance.